As we know
GtkWidget* gtk_toolbar_insert_stock (GtkToolbar *toolbar,const gchar *stock_id, const char *tooltip_text, const char *tooltip_private_text,
GtkSignalFunc callback, gpointer user_data,gint position);

is used to create an icon on the toolbar, the 2nd argument gchar *stock-id takes built-in values such as gtk-add, gtk-close etc. So is it possible to create our own stock-id for example gtk-transfer?
If so then please give me the details of its creation. Also in which file we find these stock-id's?